A motor generator functioning selectively as an electric motor and a power generator is mounted on a hybrid car or an electric automobile. Such a motor generator includes, for example, a cylindrical rotor fixed to an output shaft supported rotatably around an axis, a motor stator having an inner peripheral surface away from an outer peripheral surface of the rotor with a predetermined space provided therebetween, and a motor housing accommodating the motor stator.
A motor stator constituting such a motor generator generally includes a core member and a coil. To insulate the core member and the coil from each other, a coil is wound around a bobbin for a motor, and the bobbin around which the coil is wound is fitted to the core member.
For such a motor bobbin, for example, patent applications such as Patent Literature 1 and Patent Literature 2 have been filed so far. Such a conventional motor bobbin is generally made of a synthetic resin, and polyphenylene sulfide or the like is used, for example, in a case of a concentrated winding stator.
However, when the bobbin is made of such a synthetic resin, the lower limit of the thickness of the bobbin is said to be about 0.6 mm, and the recent further increase in efficiency, increase in power output, and reduction in size of motor generators and the like are not necessarily sufficiently coped with.
Under such circumstances and regarding the size reduction, a motor bobbin is proposed in which a bobbin body portion and flange portions are made of an insulating paper, and at least surfaces of the bobbin body portion and the flange portions made of the insulating paper to be in contact with a coil is made of an aromatic polyamide fiber (Patent Literature 3). In this technology, the insulating paper used has a structure in which heat-resistant sheets (9) and (9) made of the aromatic polyamide fiber are provided on both top and bottom sides of a substrate with adhesive agents (10) and (10) interposed therebetween. In addition, an acrylic adhesive agent or a thermosetting resin composition containing an epoxy resin component, a phenolic resin component, or an acrylic resin component, and an imidazole-based curing agent component is used as the adhesive agents.
It is said that a bobbin for a motor required to have a high efficiency and a large output has to fulfill the following four characteristics simultaneously:
1) being thin (small thickness);
2) preventing ground fault between a coil and a core member (high withstand voltage, partial discharge resistance);
3) withstanding heat generated by the coil (heat resistance); and
4) having mechanical strength. In particular, the small thickness is considered to be extremely important in the sense that the thinner the bobbin is, the more the coil can be increased, so that the space factor can be increased, and the increase in power output can be achieved.